Speed Time Distance Questions - Upstream, downstream speeds, stream speed : Ascent CAT Coaching Class, online preparation

Question 4 the day : November 17, 2003
The question for the day is from the topic Speed, Time and Distance.

Question
A man can row 50 km upstream and 72 km downstream in 9 hours. He can also row 70 km upstream and 90 km downstream in 12 hours. Find the rate of current.

1. 3 kmph
2. 8 kmph
3. 4 kmph
4. None of these

Correct Answer is 4 kmph . Choice (3) is right.

Explanatory Answer

Let x and y be the upstream and downstream speed respectively.

Hence, 50/x + 72/y = 9 and 70/x + 90/y = 12
Solving for x and y we get x = 10 km/hr and y = 18 km/hr

We know that Speed of the stream = 1/2 * (downstream speed - upstream speed)
= 1/2 (18 - 10) = 4 km/hr.

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